Motorcycle engine



FIG. 1 is a left side elevation view of the engine;

FIG. 2 is a front elevation view of the engine;

FIG. 3 is a back elevation view of the engine;

FIG. 4 is a top plan view of the engine;

FIG. 5 is a right side elevation view of the engine; and,

FIG. 6 is a bottom plan view of the engine. 

The ornamental design for a motorcycle engine, as shown and described. 